Which measurements are essential in a soft contact lens fitting?

• A. Baseline keratometry or corneal radius, refractive prescription, and lens diameter
• B. Visual acuity only
• C. Eye color and tear bilirubin
• D. Intraocular pressure and corneal thickness

Answer: (A)

Understanding how a soft contact lens fits starts with three key measurements: the cornea’s curvature, the desired lens power, and the lens diameter. The cornea’s shape, typically measured with keratometry or by estimating the corneal radius, tells you how curved the lens base should be. A base curve that matches the cornea helps the lens sit comfortably on the eye and move appropriately with each blink. The refractive prescription provides the lens power needed to correct vision, so the lens must be selected to deliver that exact correction. The lens diameter determines how wide the lens covers the cornea and interacts with the eyelids; choosing the right diameter helps ensure proper centering, tear exchange, and comfort, reducing edge lift or excessive movement.

Visual acuity by itself doesn’t reveal how a lens will sit on the eye or move with blinking, so it isn’t enough for fitting. Eye color and tear bilirubin aren’t relevant to selecting a lens. Intraocular pressure and corneal thickness relate more to eye health and other procedures than to the basic fit of a soft contact lens. By combining corneal curvature, lens power, and diameter, you align the lens with the eye’s shape, correct vision, and achieve a comfortable, stable fit.